In the printing industry, in the manufacture of paper and cardboard articles, and in similar areas of application, it is frequently necessary to provide protective varnishing of a printed medium such as cardboard or the like. The varnishing constitutes the final stage of the printing process and consists in the application of a layer of protective varnish which covers the whole surface of the printed and varnished material on or off the production line.
At the present time, indirect varnishing is carried out in the following way: a template which may be made of various types of material, such as linoleum or equivalent material, suitably coated with adhesive, is affixed to a plate designed to be applied to a rotating cylinder. The template reproduces the pattern of the areas of the medium to be varnished. For example, in the case of the production of cut-outs to form boxes, the template will have a perimeter corresponding to that of the cut-out product. The plate is then applied to the plate-cylinder. During the rotation of the plate-cylinder, the outer surface of the template is continuously in contact with the varnish. The collected varnish is transferred to the surface of a blanket cylinder. The blanket cylinder then transfers the varnish deposited on its surface directly to the medium to be processed, the transfer taking place with the aid of an opposing impression cylinder.
This method has numerous disadvantages. One of the disadvantages being that materials of the linoleum type are opaque, insufficiently soft, and consequently hard to cut.
In offset printing machines, production line printing and varnishing systems are used, with machines printing five or more colours and a coating stack with which the complete or reserved varnish is applied. For the varnishing of areas, materials of the rubber-coated fabric type (blankets) are normally used for direct varnishing. The coating is removed from the material in those areas where varnishing is not required. This system is complicated and expensive, particularly owing to the cost of the material and of the coat-removal operations. Furthermore, the rubber-coated material is opaque, and consequently the transfer of the varnish to the medium is not always optimal.